Mammalian Target of Rapamycin, mTOR, is a cell-signaling protein that regulates the response of tumor cells to nutrients and growth factors, as well as controlling tumor blood supply through effects on Vascular Endothelial Growth Factor, VEGF. Inhibitors of mTOR starve cancer cells and shrink tumors by inhibiting the effect of mTOR. All mTOR inhibitors bind to the mTOR kinase. This has at least two important effects. First, mTOR is a downstream mediator of the PI3K/Akt pathway. The PI3K/Akt pathway is thought to be over activated in numerous cancers and may account for the widespread response from various cancers to mTOR inhibitors. The over-activation of the upstream pathway would normally cause mTOR kinase to be over activated as well. However, in the presence of mTOR inhibitors, this process is blocked. The blocking effect prevents mTOR from signaling to downstream pathways that control cell growth. Over-activation of the PI3K/Akt kinase pathway is frequently associated with mutations in the PTEN gene, which is common in many cancers and may help predict what tumors will respond to mTOR inhibitors. The second major effect of mTOR inhibition is anti-angiogenesis, via the lowering of VEGF levels.
In lab tests, certain chemotherapy agents were found to be more effective in the presence of mTOR inhibitors. George, J. N., et al., Cancer Research, 61, 1527-1532, 2001. Additional lab results have shown that some rhabdomyosarcoma cells die in the presence of mTOR inhibitors. The complete functions of the mTOR kinase and the effects of mTOR inhibition are not completely understood.
Phosphatidylinositol (hereinafter abbreviated as “PI”) is one of the phospholipids in cell membranes. In recent years it has become clear that PI plays an important role also in intracellular signal transduction. It is well recognized in the art that especially PI (4,5) bisphosphate (PI(4,5)P2) is degraded into diacylglycerol and inositol (1,4,5) triphosphate by phospholipase C to induce activation of protein kinase C and intracellular calcium mobilization, respectively [M. J. Berridge et al., Nature, 312, 315 (1984); Y. Nishizuka, Science, 225, 1365 (1984)].
In the late 1980s, phosphatidylinositol-3 kinase (“PI3K”) was found to be an enzyme that phosphorylates the 3-position of the inositol ring of phosphatidylinositol [D. Whitman et al., Nature, 332, 664 (1988)].
When PI3K was discovered, it was originally considered to be a single enzyme. Recently however, it was clarified that a plurality of subtypes are present in PI3K. Three major classes of PI3Ks have now been identified on the basis of their in vitro substrate specificity [B. Vanhaesebroeck, Trend in Biol. Sci., 22, 267 (1997)].
Substrates for class I PI3Ks are PI, PI(4)P and PI(4,5)P2. In these substrates, PI(4,5)P2 is the most advantageous substrate in cells. Class I PI3Ks are further divided into two groups, class Ia and class lb, in terms of their activation mechanism. Class Ia PI3Ks, which include PI3K p110α, p110β and p100δ subtypes, are activated in the tyrosine kinase system. Class Ib PI3K is a p110γ subtype activated by a G protein-coupled receptor.
PI and PI(4)P are known as substrates for class II PI3Ks but PI(4,5)P2 is not a substrate for the enzymes of this class. Class II PI3Ks include PI3K C2α, C2β and C2γ subtypes, which are characterized by containing C2 domains at the C terminus, implying that their activity will be regulated by calcium ions.
The substrate for class III PI3Ks is PI only. A mechanism for activation of the class III PI3Ks is not clarified yet. Because each subtype has its own mechanism for the regulating activity, it is considered that the respective subtypes will be activated depending on their respective stimuli specific to each of them.
In the PI3K subtypes, the class Ia subtype has been most extensively investigated to date. The three subtypes of class Ia are hetero dimers of a catalytic 110 kDa subunit and regulatory subunits of 85 kDa and 55 kDa. The regulatory subunits contain SH2 domains and bind to tyrosine residues phosphorylated by growth factor receptors with a tyrosine kinase activity or oncogene products, thereby inducing the PI3K activity of the p110 catalytic subunit. Thus, the class Ia subtypes are considered to be associated with cell proliferation and carcinogenesis. Furthermore, the class Ia PI3K subtypes bind to activated ras oncogene to express their enzyme activity. It has been confirmed that the activated ras oncogene is present in many cancers, suggesting a role of class Ia PI3Ks in carcinogenesis.
There are three mTOR inhibitors, which have progressed into clinical trials. These compounds are Wyeth's Torisel, also known as 42-(3-hydroxy-2-(hydroxymethyl)-rapamycin 2-methylpropanoate, CCI-779 or Temsirolimus; Novartis' Everolimus, also known as 42-O-(2-hydroxyethyl)-rapamycin, or RAD 001; and Ariad's AP23573 also known as 42-(dimethylphopsinoyl)-rapamycin. The FDA has approved Torisel for the treatment of advanced renal cell carcinoma. In addition, Torisel is active in a NOS/SCID xenograft mouse model of acute lymphoblastic leukemia [Teachey et al, Blood, 107(3), 1149-1155, 2006]. Everolimus is in a phase II clinical study for patients with Stage 1V Malignant Melanoma. AP23573 has been given orphan drug and fast-track status by the FDA for treatment of soft-tissue and bone sarcomas.
The three mTOR inhibitors have non-linear, although reproducible pharmacokinetic profiles. Mean area under the curve (AUC) values for these drugs increase at a less than dose related way. The three compounds are all semi-synthetic derivatives of the natural macrolide antibiotic rapamycin. It would be desirable to find fully synthetic compounds, which inhibit mTOR that are more potent and exhibit improved pharmacokinetic behaviors.
As explained above, mTOR inhibitors and PI3K inhibitors are expected to be novel types of medicaments useful against cell proliferation disorders, especially as carcinostatic agents. Thus, it would be advantageous to have new mTOR inhibitors and PI3K inhibitors as potential treatment regimens for mTOR- and PI3K-related diseases. The instant invention is directed to these and other important ends.